If you’re a fruit fly, tease your mind with this optical illusion. Humans welcome too.

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Rotat­ing snake illu­sion. Cred­it: Akiyoshi Kitaoka

Please move your gaze around the image, rest­ing from time to time.

Then, fix your gaze at a point, and see what happens.

You will prob­a­bly first see ‘snakes’ rotat­ing, some clock­wise, oth­ers anti­clock­wise, and then stop. In fact, it’s just an sta­tion­ary image — noth­ing is mov­ing at all.

Visu­al per­cep­tion is cre­at­ed by our brain’s inter­pre­ta­tion of visu­al infor­ma­tion. Our minds active­ly inter­pret per­cep­tu­al input, rather than pas­sive­ly record it — make sure to remem­ber that next time you have a dis­agree­ment with someone!

On human perception and fruit flies:

Which opti­cal illu­sions can ani­mals see? (Nat­Geo):

VISUAL ILLUSIONS REMIND us that we are not pas­sive decoders of real­i­ty but active inter­preters. Our eyes cap­ture infor­ma­tion from the envi­ron­ment, but our brain can play tricks on us. Per­cep­tion doesn’t always match reality.

Sci­en­tists have used illu­sions for decades to explore the psy­cho­log­i­cal and cog­ni­tive process­es that under­lie human visu­al per­cep­tion. More recent­ly, evi­dence is emerg­ing that sug­gests many ani­mals, like us, can per­ceive and cre­ate a range of visu­al illusions…

In an August study in Pro­ceed­ings of the Nation­al Acad­e­my of Sci­ences, for exam­ple, Yale researchers showed that fruit flies, like humans, can be fooled into see­ing motion in an image where there is none, such as the rotat­ing snake illu­sion, well-known to neu­ro­sci­en­tists and psy­chol­o­gists … The more sci­en­tists look—in the lab and in nature—the more sim­i­lar­i­ties they’re find­ing between how humans and ani­mals per­ceive the world.

The Study:

Mech­a­nism for anal­o­gous illu­so­ry motion per­cep­tion in flies and humans (PNAS). From the Abstract:

  • Sig­nif­i­cance: Most of the time, visu­al cir­cuit­ry in our brains faith­ful­ly reports visu­al scenes. Some­times, how­ev­er, it can report motion in images that are in fact sta­tion­ary, lead­ing us to per­ceive illu­so­ry motion. In this study, we estab­lish that fruit flies, too, per­ceive motion in the sta­tion­ary images that evoke illu­so­ry motion in humans. Our results demon­strate how this motion illu­sion in flies is an arti­fact of the brain’s strate­gies for effi­cient­ly pro­cess­ing motion in nat­ur­al scenes. Per­cep­tu­al tests in humans sug­gest that our brains may employ sim­i­lar mech­a­nisms for this illu­sion. This study shows how illu­sions can pro­vide insight into visu­al pro­cess­ing mech­a­nisms and prin­ci­ples across phyla.

More fun illusions and brain teasers: